Karl Landsteiner classifies the main human blood groups as A, B, AB and O

US geneticist Thomas Hunt Morgan establishes the chromosome theory of heredity through his study of the fruit fly Drosophila melanogaster

Martha, 29 years old and the last passenger pigeon in the world, dies in the Cincinnati zoo in Ohio

Canadian physiologists Frederick Banting and Charles Best isolate insulin from the pancreas for the treatment of diabetes

Biology teacher John Scopes is prosecuted for breaking state law by teaching evolution to his class of children in Dayton, Tennessee

Austrian zoologist Karl von Frisch demonstrates that bees communicate the whereabouts of food by means of a dance

Scottish bacteriologist Alexander Fleming accidentally discovers a mould that selectively kills bacteria, and calls it penicillin

The Austrian zoologist Konrad Lorenz describes his experiments on young geese, with their capacity to imprint on human beings

German-born British scientist Hans Krebs discovers the biochemical cycle that becomes known by his name

US psychologist B.F. Skinner trains laboratory rats to use their brains in his 'Skinnner box'

Karl von Frisch demonstrates that bees make use of the polarized light of the sun to calculate direction

Molecular biologists Francis Crick and James Watson announce their discovery of the double-helix structure of DNA

US environmentist Rachel Carson publishes Silent Spring, an impassioned warning of ecological disaster

Luc Montagnier, at the Pasteur Institute in Paris, discovers a new human retrovirus that he names LAV (later changed to HIV)

Genetic (or DNA) fingerprinting is invented and developed by British geneticist Alec Jeffreys

The Human Genome Project begins in the US Department of Energy, with the aim of sequencing the whole of human DNA

Mad Cow Disease (BSE, or bovine spongiform encephalopathy ) is identified and described in Britain

British primatologist Jane Goodall publishes Through a Window, exposing violence and brutality in chimpanzees

A fatal variant CJD (Creutzfeldt-Jacob disease) is first identified in Britain, linked to BSE but capable of infecting humans

Dolly the Sheep is cloned in an epoch-making experiment at the Roslin Institute in Edinburgh

Chromosome 22 becomes the first human genome to be fully sequenced, at the Sanger Institute in Cambridge, England

A White House ceremony celebrates a full draft of the human genome completed by two rival projects

Leland Hartwel, Paul Nurse and Tim Hunt win the Nobel Prize for their discoveries of key regulators of the cell cycle